With the recent trend toward higher integration and higher performance of ceramic wiring boards for mounting LSIs, it has been attempted to make finer geometries of wirings and to make narrower pitches of via-wirings. As a structure of a typical wiring circuit board of this type, there is known a structure in which a thin film circuit is laminated on a thick film circuit board. A technology to which the above structure pertains is disclosed, for example, in "Microelectronics Packaging Handbook (edited by Rao R. Tummala, Eugene J. Rymaszewski), p.14, published by Nikkei PB Co., Ltd. (March, 1991)".
The above-described prior art, however, has the following three disadvantages:
(1) Upon formation of a thin film circuit on a ceramic board containing wirings, it is necessary to connect conductors on the ceramic board side to the thin film circuit. The number of the connecting points therebetween becomes enormous for a large-sized board having high density wirings, and also, in the ceramic board, the above connecting points may be displaced with a variation at steps of printing wirings to green sheets, laminating the green sheets, and sintering the laminated green sheets. As a result, it is difficult to connect all of the connecting points between the conductors on the ceramic board side and the thin film circuit without any problem.
(2) If the above ceramic board contains defects such as short-circuit and/or disconnection of wirings, the defects must be corrected before connection of the conductors on the ceramic board side to the thin film circuit; however, it is not easy to correct the defects.
(3) In the case where a conducting material such as copper, chromium, or nickel is used in combination with an organic insulating material such as polyimide for forming a thin film circuit on a ceramic board, there occurs a problem that a film made from the organic insulating material such as polyimide may be cracked due to film stress of a film made from the conducting material.
The present inventors have undertaken studies to solve all of the above problems (1) to (3) and to realize a circuit board with a high density and a high reliability and a method of manufacturing the circuit board, and accomplished the present invention.